*,
*:before,
*:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.container {
  display: flex;
  flex-flow: row nowrap;
  height: 100vh;
  align-items: stretch;
}
.container .ctrl {
  flex: 400px 0 0;
  padding: 1em;
  background-color: #3b4393;
  color: #fff;
}
.container .ctrl h1{
  text-align: center;
  text-shadow: 2px 2px 4px rgba(0,0,0,.5);
}
.container .prev {
  flex: 600px 3 1;
  padding: 1em;
}